Fix prober for skiamonitor, as the golang http client follows redirects.
Fix prober for skiamonitor, as the golang http client follows redirects.

BUG=skia:

Review URL: https://codereview.chromium.org/842653002

google/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot